This invention relates to a method of manufacturing a large size single crystal silicon rod from a silicon melt in a protective atmosphere by the pulling method or Czochraski method and an apparatus for said method.
The prior art apparatus for manufacturing a single crystal silicon rod by the pulling method is constructed roughly as shown in FIG. 1. Reference numeral 1 denotes a vessel provided with an inlet 2 of protective gas and and outlet 3 thereof. A quartz crucible 5 in which a silicon melt 4 is to be produced is set in the vessel 1. The quartz crucible 5 is supported by a holding member 6 made of graphite placed around the holding member 6 is a graphite heater 7. Provided further outside of the graphite heater 7 is a heat-insulating member 8 made of, for example, graphite felt. Reference numeral 9 denotes a pulling bar, the inner end of which holds a seed silicon crystal 11 by means of a fixing device 10. A single crystal silicon rod 12 is produced by dipping the seed silicon crystal 11 in the silicon melt 4 and pulling said seed silicon crystal 11 out of said melt 4 with the temperature and the speed at which the seed silicon crystal 11 is to be pulled up controlled to the desired level. Reference numeral 13 represents a shaft for rotating the quartz crucible 5. While the seed silicon crystal 11 is pulled up, the rotation of the quartz crucible 5 by the shaft 13 is controlled to such speed as produces a single crystal silicon rod of uniform quality.
A substantially dislocation-free single crystal silicon wafer is generally manufactured by heating a single crystal silicon rod grown in the apparatus of FIG. 1 at a temperature of 600.degree. to 700.degree. C. for about one hour, followed by quenching and forming the produced single crystal silicon rod into a wafer having a thickness of 300 to 650 microns by machining and chemical etching.
The dislocation density of a single crystal silicon wafer is indicated by counting a number of pits appearing as the result of chemical etching by means of an optical microscope. In general, a thin single crystal silicon wafer whose polished surface contains 500 or fewer etch pits per cm.sup.2 is referred to as a dislocation-free product.
Even with the so-called dislocation-free single crystal silicon wafer, it is experimentally shown that while heat treatment is repeated several times at a temperature of 800.degree. to 1200.degree. C. during the manufacture of a semiconductor element, various lattice defects including the dislocation thereof take place in silicon crystal, resulting in a decrease in the yield of a semiconductor device. It has been discovered that with the same type of dislocation-free single crystal silicon product, lattice defects appear prominently or substantially unnoticeably during the manufacture of a semiconductor device, depending on the condition in which the preceding single crystal silicon rod is grown.